The present invention relates to an adhesive sheet and, more particularly, to an adhesive sheet which provides facile formation of printing thereon by means of a xerographic recording system such as a non-impact printer, a Kanji printer (i.e., printer which is excellent in resolving power and which is used for recording characters such as Chinese characters), a copier and the like.
Adhesive sheets are in wide use for commercial, office and home application in the form of labels, seals, stickers, emblems, etc.
The adhesive sheet comprises a pressure-sensitive adhesive layer formed between a surface sheet and a release sheet. The surface sheet can be paper, film, metal foil or the like. The release sheet base material can be high density paper such as glassine paper, or clay-coated paper, polyethylene laminated paper or like similar paper, and a release agent such as silicone compounds or fluorine compounds is coated thereon. The clay-coated paper has a clay-coated layer as an undercoat layer over the surface of paper and the polyethylene laminated paper has a polyethylene film laminated as an undercoat layer over the surface of paper. As the pressure-sensitive adhesives, rubber-type, acrylic type, vinyl ether-type adhesives are used in the form of emulsion-type, solvent-type or non-solvent-type composition.
With the development of the information society, demand for the adhesive sheets has been rapidly increasing, particularly for the adhesive sheets useful for printers employing zerography such as a non-impact printer, a Kanji printer, etc.
Heretofore, glassine paper has been used as a release sheet base material of the adhesive sheets used for the above application. However when high density paper with high degree of beating such as glassine paper is used for a Kanji printer, failure in paper feed or in stacking, misregistration in printing and like problems tend to occur. This type of paper is hypersensitive to heat because of its higher degree of shrinkage during drying compared with other ordinary paper. As a result, the paper further shrinks by the action of heat applied during fixation of toner, and a curl of the sheet occurs, thereby causing the above problems. Further, the stacking of the paper is not satisfactorily done by an automatic folding stacker due to high stiffness of the paper. Furthermore, uneven moisture absorption takes place after the fixation of toner by heating, thereby easily causing cockle, curl and the like. Moreover, the blocking of toner is likely to occur since the paper does not rapidly dissipate heat.
Also another problem is the removal of adhesive labels from the release sheet due to insufficient adhesion during transfer or fixation of toner in the printer (i.e., during passing through the parts of the printer having high curvature).
Various methods to correct the curls of adhesive sheet have been proposed in the field of the adhesive sheet. The proposed methods are, for example, the use of a curl breaker whereby a curl in a certain direction is acutely coiled to the reverse direction, the use of an air conditioner, the damping with steam and the like. Up to now, however, these methods entail complicated process with only insufficient effects, thus failing to provide satisfactory results.